1. Field of the Invention
The present invention relates to a surface acoustic wave device, and more particularly to a package having a surface acoustic wave element with electrode pads turned face down.
2. Description of the Related Art
Some surface acoustic wave elements mounted in packages are used as surface acoustic wave filters. One technical concept of a package housing a surface acoustic wave element with electrode pads turned face down is disclosed in U.S. patent application Ser. No. 07/721,823 entitled "Surface acoustic wave device and its manufacturing method" now U.S. Pat. No. 5,252,882 issued Oct. 12, 1993. In the disclosed arrangement, electrode pads of the surface acoustic wave device and electrode pads of the package are connected by gold bumps. The disclosed package is smaller in size and more expensive to manufacture than packages where electrode pads are connected by wire bonding.
The disclosed package will now be described below with reference to FIGS. 1 through 3.
As shown in FIG. 1, a package 1 with a surface acoustic wave element S mounted therein comprises a rectangular bottom plate 2, a surrounding side wall 3 mounted on a peripheral edge of the bottom plate 2, and a cover 4 mounted on the side wall 3. The side wall 3 is formed by blanking a workpiece. Wiring conductors, including electrode pads 5, are disposed on an upper surface of the bottom plate 2 by printing. The surface acoustic wave element S is mounted in the package 1 by bumps 6 on the electrode pads 5 by way of facedown bonding. The surface acoustic wave element S has electrode pads 7 on its lower surface.
To connect the electrode pads 5 on the bottom plate 2 and the electrode pads 7 of the surface acoustic wave element S, it is necessary to position the surface acoustic wave element S with respect to the package 1 very accurately. This is because poor electric connection would be achieved between the electrode pads 5 and 7 if they were relatively misaligned.
As shown in FIG. 2, the side wall 3 that is formed by blanking, has inner corners 3a, 3b, 3c, 3d which are round so as to minimize the development of microcracks therein. To be able to insert the surface acoustic wave element S into the side wall 3, the size of the surface acoustic wave element S or the size of the package 1 should be designed taking into account the round surfaces of the corners 3a, 3b, 3c, 3d of the side wall 3, so that the round corners 3a, 3b, 3c, 3d and the corners of the surface acoustic wave element S will not be damaged by contact with each other. To meet such a requirement, it is necessary to increase the gap L (see FIG. 3) between the outer side surface of the surface acoustic wave element S and the inner side surface of the side wall 3, resulting in a relatively large package size. If the gap L is relatively large, however, the surface acoustic wave element S tends to be dislocated when mounted, shifting the electrode pads 5, 7 out of alignment with each other. As a result, the desired electric conduction cannot be accomplished between the electrode pads 5 and 7.